iwlwifi: mvm: fix a race in CSA that caused assert 0x3420

iwlwifi: mvm: fix a race in CSA that caused assert 0x3420

When we get a channel switch with a very long quiet period, we schedule
a work to disconnect after a while. This work runs in background. In the
meanwhile, we keep getting beacons and sending FW modify command for each.
This has a potential race, where we modify the CSA after we aborted it.

Protect the flow by setting csa_failed to true in case we abort, and check
it before sending the modify command.

This required a modification to the way we treat csa_failed in
iwl_mvm_post_channel_switch:
1. The variable isn't being reset anymore, so we can still look at it in
iwl_mvm_channel_switch_rx_beacon. This is fine, since we reset it when
starting a new CSA.
2. There is no more early return in case of csa_failed. This is fine,
since before this patch csa_failed was set only for GO, and for GO the
function is only resetting the power settings, which we want to restore
even in case of failure.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201209231352.b023856bdf39.I4ed0149e0018fe5e1ae3c2a1cbc614954016063f@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>